This invention relates to an optical reader for scanning a surface to be scanned by using an information beam ray such as a laser beam ray and optically reading recorded information such as a bar code recorded on the surface to be scanned.
Heretofore, there has been known an optical reader, wherein an optical beam emitted from a laser light source is guided to a scanning rotary multiface mirror, the optical beam being swung in the rotating direction of the scanning rotary multiface mirror to scan a surface of an object to be measured in which bar code etc. are recorded. The information beam reflected from the surface to be scanned being condensed and guided to an opto-electric transforming means for opto-electrically transferring the same in order to optically read information recorded on the surface to be scanned.
There are two types of conventional optical readers; one is the entire scanning area condensing system which includes as light condensing means a condensing lens for condensing and imaging the information beam reflected from the surface to be scanned on a light receiving surface of an opto-electric transforming mean. Light in the entire scanning area is condensed as an information beam by the condensing lens irrespective of location of a part illuminated by the information beam in the scanning direction of the surface to be scanned. The other is the illuminating part condensing system wherein the information beam is reflected again by a scanning rotary multiface mirror and guided to an opto-electric transforming system. In this second system only the information beam from an illuminating part of the surface to be scanned which is illuminated by the optical beam is received.
An optical reader employing the illuminating part condensing system is constituted such that a perforated mirror for dividing an optical path is disposed between a laser light source and a scanning rotary multiface mirror. The optical beam being projected through the perforated portion of the perforated mirror, and an information beam reflected from a surface to be scanned being reflected by the scanning rotary multiface mirror and perforated mirror to be guided to an opto-electric transforming means.
Since the conventional optical reader of the entire scanning area condensing system is constituted such that outer light other than the optical beam is also read as an information beam, peripheral outer light is taken in as an undesirable noise portion. Accordingly, when peripheral illumination of the surface to be scanned illuminated by a room illumination is large, it cannot read the information beam as a signal due to adverse affection of the peripheral illumination.
In the conventional reader employing the illuminating part condensing system, a scanning optical path of an optical beam and a reflection optical path thereof are identical between the perforated mirror and the surface to be scanned. Accordingly, it has the disadvantage that diffracted light of the projected optical beam diffracted by the perforated portion of the perforated mirror and scattered light scattered by the scanning rotary multiface mirror and other optical parts are guided as a noise portion directly to the opto-electric transforming means. Further, the information beam is received through the reflecting surface of the perforated mirror. Accordingly, it has the disadvantage that the information light beam guided to the opto-electric transforming means is limited in quantity.
Furthermore, in the case optical members such as a reflecting prism, etc. are disposed within the scanning optical path so that the projected optical beam is divided into a plurality of scanning beams to draw a plurality of scanning paths on the surface to be scanned, the information beam to be received is also limited by these optical members which makes it difficult to increase the quantity level of the information beam to be received.